Process for the preparation of



United States Patent 3,035,101 PROCESS FOR Tll-E PREPARATION OF MONONITROOLEFINS Wolfgang K. Seifert, Berkeley, and Louis L. Ferstandig,

El Cerrito, Califi, assignors to California Research Corporation, San Francisco, Calif, a corporation of Delaware No Drawing. Filed June 2, 1961, Ser. No. 114,291 3 Claims. (Cl. 260-644) The process of this invention provides a method of preparing mononitroolefins from a nitrogen tetroxideolefin addition product. More specifically, the process of this invention comprises the reaction of a tertiary amine having a pK below about 9 with a nitrogen tetroxideolefin addition product. The mononitroolefin prodnets of this invention are particularly useful as chemical intermediates.

It has long been known that organic nitrogen compounds may be prepared by the addition of nitrogen tetroxide to an olefin. US. Patents 2,384,047, 2,384,048, and 2,472,550, are exemplary of the prior art processes for the preparation of these nitrogen compounds from olefins. This reaction, as is known in the art, may be carried out either in the presence or absence of oxygen, or in the presence or absence of a solvent, such as an ether or ester-type solvent which complexes with the nitrogen tetroxide. 'It has been found, however, that the formation of certain undesirable oxidation by-products, such as nitrate esters of Z-hydroxycarboxylic acid, furazan derivatives, and bis-nitroso compounds, may be minimized by using both oxygen and an ether or ester-type solvent in the reaction.

Various methods have been proposed to prepare mononitroolefins from the nitrogen tetroxide-olefin addition product, prepared as above described. For example, US. Patent 2,495,424 teaches the reaction of ammonia or urea with the crude addition product to form the mononitroolefin. Although this process is suitable for branched-chain olefins, such as 2,4,4-trimethylpentene-l and isobutene, as described in the examples of that patent, it has been found that the yield of mononitroolefin prepared from the addition product of nitrogen tetroxide and normal, straight-chain olefins, using the processes of the prior art, is substantially reduced, rendering these processes commercially impractical for the production of straight-chain mononitroolefins.

In contradiction to the prior art processes, it has now been discovered that a high yield of mononitroolefin may be obtained from a nitrogen tetroxide-olefin addition product irrespective of the type of olefin used therein if this addition product is reacted under substantially anhydrous conditions at a temperature from about 50 to +50 C., preferably l() to +25 C., with a tertiary amine having a pK, below about 9, preferably about 4 to 5.

The choice of a particular amine is not critical, although a tertiary amine is required. It has been found that tertiary amines having a pK above about 9 are not sumciently effective to form reasonably high yields of the mononitroolefin. However, any tertiary amine which has a pK below about 9 is considered satisfactory for the process of this invention. As examples, triethylamine, trimethylamine, dimethylbenzylamine, diethylbenzylamine, tripropylamine, pyridine, etc, are suggested, the non-cyclic, and especially the lower alkyl, amines being preferred.

In a preferred embodiment of the invention, the nitrogen tetroxide-olefin addition product is prepared in the presence of both oxygen and a solvent. Accordingly, an' ethereal solution of nitrogen textroxide is prepared by absorbing the nitrogen tetroxide gas into the solvent,

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2 e.g., ether. The ethereal solution may then be added to an olefin or olefin mixture, or preferably, the olefin added to the ethereal solution. During the addition, oxygen gas or air is continuously bubbled into the mix-' ture. It has been found that to have an appreciable eifect in inhibiting side reactions, the mol ratio of feed oxygen to olefin should be at least 1:250, preferably 1:100 to about 1:25. The reaction is exothermic, and hence careful temperature regulation is required. The reaction is carried out from about -5() to +25 C., preferably -l0 to +10 C. At lower temperatures the rate is too slow, and at higher temperatures the nitrogen tetroxide distills out of solution. Temperature control is easily obtained by any conventional cooling means, such as an ice bath. For optimum yields, it is preferred to have the reaction substantially anhydrous, thus employing only anhydrous ether and using conventional drying means, such as P 0 drying tubes, to maintain anhydrous conditions. The mol ratio of nitrogen tetroxide to olefin should be about 1:1, although a slight excess of nitrogen tetroxide is preferable.

To ensure a complete addition of nitrogen tetroxide to olefin, the temperature may be raised to about l5--20 C. for a short period of time, about one-half hour, after all of the olefin has been added. The reaction mixture may, if desired, then be diluted with additional ether since it has been found easier to reduce the degree of side reac: tions, especially in batch processes, by employing a more dilute solution.

To this solution of nitrogen-containing compounds, as above prepared, a tertiary amine is added. An approximately equimolar ratio of amine to nitrogen tetroxide: olefin addition product is satisfactory, although an excess of amine is preferable. Accordingly, a mol ratio of amine to addition product of from about 1:1 to 2:1 provides excellent yields of nitroolefin. This reaction too is exothermic; hence the temperature should be maintained between about -50 to +50 C., preferably -10 to +25 C. Temperature control may be effected by means of an ice bath. Temperatures below this range result in slower rates of reaction, and higher temperatures promote undesirable side reactions.

Complete reaction occurs in a very short time; a time of less than 10 minutes has been found satisfactory. If desired, the reaction may be finished by maintaining a temperature of about 20-25" C. for about one-half hour before completing the reaction. After this time the reaction is stopped by the addition of an acid, e.g., dilute sulfuric acid or acetic acid, to react with the excess amine. Any ionic materials then present are dissolved in water which is added to the reaction mixture. An extraction with ether removes an ethereal solution of nitroolefin product. This ethereal solution may be washed with a slightly basic wash solution, such as sodium bicarbonate, to remove any acetic acid, and then washed with water. The washed ethereal solution of product is then vacuumdistilled to remove the ether, leaving the purified nitroolefins in high yields, up to 70 to percent based on olefin starting material. I 7

Without intent of placing any further limitations on the invention as hereinbefore described, the following examples are given to illustratethe invention in more detail. Examples 1 and 2 show that the same result may be obtained irrespective ofwhether the addition of olefin and nitrogen tetroxide to other is carried out simultaneously or consecutively.

Example 1 0.10 mol n-octadecene and 0.11 mol of an oxygen-saturated ethereal solution of nitrogen tetroxide were slowly admixed at 22l C. for about 35 minutes, maintaining the nitrogen tetroxide always in excess. During this period, about 0.002 mol oxygen was simultaneously bubbled through the reactants. The reaction was allowed to continue for about 1 /2 hours after the addition was completed, keeping the temperature at about 12-20 C. The concentration of the addition product in diethyl ether solvent was about 10 parts by weight addition product per 7 parts ether.

Ether was then added to reduce the concentration of the addition product to about 10 parts by weight addition product per 60 parts ether. To this diluted mixture, 2 mols triethylamine were added per mol of olefin used to Form the addition product at a temperature of about 2 to +3 C. over a period of about 5 minutes. After addition of the amine, the temperature was allowed to rise to about 24 C. for /2 hour. The mixture was cooled to about C. and quenched by the addition of 200 ml. cold 2 N sulfuric acid while agitating the mixture. The product was extracted with ether and the ethereal solution washed with sodium bicarbonate and water. The ether was vacuum evaporated and the residue chromatographed on silicic acid yielding 75 percent analytically pure l-nitrooctadecene based on olefin charge.

Example 2 0.30 mol n-octadecene was added to 0.31 mol of an oxygen-saturated ether'al solution of nitrogen tetroxide at 2-21" C. over about 40 minutes while about 0.002 mol oxygen was simultaneously bubbled through the reactants. The reaction was allowed to continue for about 35 minutes after the addition was completed, keeping the temperature at about C. The concentration of the addition product in diethyl ether solvent was about 10 parts by Weight addition product per 7 parts ether.

Ether was then added to reduce the concentration of the addition product to about 10 parts byweight addition product per 60 parts ether. To this diluted mixture, 2 mols triethylamine were added per mol of olefin used to form the addition product at a temperature of about 4- 10 C. over a period of about 5 minutes. After addition of the amine, the temperature was allowed to rise to about 22-24" C. for /2 hour. The mixture was cooled to about 10-20 C. and quenched by the addition of 200 ml. cold 2 N sulfuric acid while agitating the mixture. The product was extracted with ether and the ethereal solution washed with sodium bicarbonate and water. The ether was vacuum evaporated and the residue chromatographed on silicic acid yielding 77 percent analytically pure l-nitrooctadecene based on olefin charge.

Example 3 To demonstrate the effect of other tertiary amines, 1000 mg. of pyridine were added to 70-400 mg. l-nitro- 2octadecylnitrite, one of the products obtained by the addition of nitrogen'tetroxide to an olefin, at a tempera ture of 23 C. The mixture was allowed to react for a period of about 2 hours, and was then quenched by the addition of 200 ml. cold 2 N sulfuric acid while agitating the mixture. The product was extracted with ether and the ethereal solution washed with sodium bicarbonate and water. The ether was evaporated and the residue analyzed by quantitative IR analysis, showing a content of l-nitro-l-octadccene of about 80-90 percent, thus showing that pyridine, a tertiary amine having a pK of about 8.85, is within the scope of tertiary amines of this invention.

Example 4 0.40 mol cyclooctene was added to an oxygen-saturated ethereal solution containing 0.43 mol of nitrogen tetroxide at 912 C. over about 24 minutes while about 0.013

mol oxygen was simultaneously bubbled through the mixture. The reaction was allowed to continue for about minutes after the addition was completed, keeping the 5 temperature at about 13 C. The concentration of the addition product in diethyl ether solvent was about 1 part by weight addition product per 2 parts ether.

To this mixture 3 mols triethylamine were added per mol of olefin used to form the addition product at a temperature of about 412 C. over a period of about 12 minutes. After addition of the amine, the temperature was allowed to rise to about 24 C. for minutes. The mixture was cooled to about 3 C. and quenched by the addition of 150 ml. ether and 72 g. acetic acid while agitating the mixture. 200 ml. water were then added and the mixture was extracted with ether and the ethereal solution washed twice with water, twice with sodium bicarbonate, and three additional times with water. The ether was vacuum evaporated and the residue, weighing 61 g., was analyzed by quantitative IR to be 93 percent pure l-nitrocyclooctene, which represents over 90 percent yield based on olefin charged. The l-nitrocyclooctene was purified and the pure product, boiling at 60 C. at 0.2 mm. Hg, was analyzed as follows:

The process of the invention operates on any olefin having at least one hydrogen on one of the unsaturated carbon atoms. The olefin may also have open chain substituents, e.g., alkyl, or cyclic substituents, such as cycloaliphatic substituents, or may itself be part of a cyclic system, e.g., a cycloalkene. Preferably the olefin is selected from the class consisting of normal l-alkenes and cycloalkenes, particularly unsubstituted cyeloalkenes, e.g., propylene, n-l-butene, n-l-pentene, n-l hexene, n-l-heptene, n-1-octene, n-l-nonene, n-l-decene, n-l-undecene, n-l-dodecene, n-l-tridecene, n-l-tetradecene, n-l-pentadecene, n-l-hexadecene, n-l-heptadecene, n-l-octadecene, n-l-nonadecene, n-l-eicosene, cyclopente'ne, cyclohexene, cycloheptene, cyclooctene, cyclononene, cyclodecene, cycloundecene, cylododecene, etc.

As will be evident to those skilled in the art, various modifications :on this process can be made or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the -disclosure or from the scope of the following claims.

This application is a continuation-in-part of copending application Serial No. 96,114, filed March 16, 1961.

We claim:

1. A process for the production of mononitroolefins which comprises reacting a tertiary amine having a pK below about 9 under substantially anhydrous "conditions at a temperature in the range of about 50 to +50 C. with a nitrogen tetroxide-olefin addition product.

2. A process for the production of mononitroolefins which comprises reacting a tertiary amine having a'pK below about 9 under substantially anhydrous conditions at a temperature in the range of about 50 to +50 C. with the reaction product of nitrogen tetroxide and an olefin reacted in the presence of oxygen introduced in a mol ratio of oxygen to olefin of at least 1:250.

3. l-nitrocyclooctene.

No references cited. 

1. A PROCESS FOR THE PRODUCTION OF MONONITROOLEFINS WHICH COMPRISES RACTING A TERTIARY AMINE HAVING A PKB BELOW ABOUT 9 UNDER SUBSTANTIALLY ANHYDROUS CONDITIONS AT A TEMPERATURE IN THE RANGE OF ABOUT -50* TO +50* C. WITH A NITROGEN TETROXIDE-OLEFIN ADDITION PRODUCT. 